Shares of Atara Biotherapeutics (NASDAQ:ATRA) plunged about 55% on Monday after the U.S. Food and Drug Administration delivered a Complete Response Letter declining to approve the company’s cancer therapy submission.
The FDA rejected EBVALLO (tabelecleucel), Atara’s treatment for Epstein-Barr virus–positive post-transplant lymphoproliferative disease (EBV+ PTLD) in patients who have previously received therapy. In its response, the regulator said the single-arm ALLELE study did not provide sufficient evidence of effectiveness to support accelerated approval.
The decision marks a major setback for Atara, which said the FDA had earlier indicated that the trial design was acceptable. According to the company, the agency’s stance now runs counter to guidance it had received over the past five years.
“We are surprised and disappointed by this FDA decision for EBV+ PTLD patients who have a significant unmet need, highlighted by tabelecleucel’s Orphan Drug designation and by the granting of Breakthrough status at the time we submitted the ALLELE primary data,” said Cokey Nguyen, President and CEO of Atara.
The FDA acknowledged that previously cited Good Manufacturing Practice compliance issues had been addressed and confirmed that no new safety concerns were identified in the latest review.
Atara transferred the Biologics License Application to Pierre Fabre Pharmaceuticals in November 2025. The two companies said they plan to request a Type A meeting with the FDA within 45 days to discuss potential next steps.
The regulatory setback comes amid mounting financial pressure for Atara. As of December 31, 2025, the company reported cash, cash equivalents and short-term investments of approximately $8.5 million. In response to funding constraints, Atara carried out extensive cost-reduction measures during 2025, including cutting its workforce by around 90%.